The copper-based catalyst has been known to be used as a hydrogenation catalyst. For example, it has been used as the hydrogenation catalyst for making alcohols. For another example, it has been used for reductive alkylation for making p-phenylenediamine derivatives, including N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, N-isopropyl-N′-phenyl-p-phenylenediamine, and N-sec-octyl-N′-phenyl-p-phenylenediamine, which are rubber antidegradants. The derivatives are made by reacting 4-aminodiphenylamine with a ketone, which, depending on the desired derivative, may be acetone or methyl isobutyl ketone, etc., in the presence of hydrogen and the catalyst under suitable reaction conditions for N-alkylation. The copper-based catalyst is inexpensive and has been widely used for hydrogenation reactions.
Methods for making and activating the copper-based catalyst, mainly as the hydrogenation catalyst for making alcohols, are known. For examples, see U.S. Pat. Nos. 4,436,833; 4,780,481; 4,791,141; 5,591,873; 5,554,574; 5,481,048; 5,658,843; and 6,410,806. U.S. Pat. No. 7,807,603 relates to a catalyst extrudates based on copper oxide and their use for hydrogenating carbonyl compounds. U.S. Pat. No. 5,817,872 relates to a copper catalyst for the hydration of nitrile and the preparation thereof. U.S. Pat. No. 7,037,877 relates to a process for preparing copper chromite catalyst. U.S. Pat. No. 5,097,071 relates to a supported copper catalyst, process for preparing the catalyst, and process for preparing N-alkylated aromatic amines using the copper catalyst. In these patents, the copper-containing catalysts are treated or activated by an oxidizing or reducing reagent following the preparation steps. However, none of the patents address the problem encountered in using the copper-based catalyst as the hydrogenation catalyst for the N-alkylation for making the p-phenylenediamine derivatives.
When the active copper-based catalyst is used for the N-alkylation for making p-phenylenediamine derivatives, it exhibits poor selectivity and the reaction produces abundant side products and impurities. These side products and impurities mix with the final product and lower the quality of the product; they are difficult to separate and may cause the entire product batch to become waste and total loss of the catalyst.